1. Field of the Invention
The present invention relates to an apparatus for detecting the battery voltage which decreases below the value of the reference voltage.
2. Brief Description of the Prior Art
In recent years, there have been increased number of apparatus driven by the battery. The same tendency is seen also in the field of office machines, and there are many types which are driven by the battery equipped in the own apparatus for the reason of small-sized and portable requirement. The battery voltage can be sometimes lowered to cause the apparatus not to perform the normal operations. Accordingly, it is also provided with some apparatus, which are equipped with a battery voltage detecting device for detecting whether the battery voltage is lowered below the reference voltage value, that is, the low battery condition, to prevent the above-mentioned disadvantage.
FIG.5 is the block diagram of a conventionally typical low battery detecting system in a recording apparatus. Hereinafter, it is described the operation sequence thereof:
(1) sampling the terminal voltage V.sub.battery of a battery 9 by the detector means 2 in timing of every printing operation; PA1 (2) converting the detected voltage V.sub.battery to a digital value X.sub.battery by the A/D converter means 3; PA1 (3) comparing means 5 compares X.sub.battery with a predetermined value X.sub.low ;and PA1 (4) based on the result above, a microprocessing unit determines whether the condition of the battery is low battery or not, whereby usually, when X.sub.battery is lower than X.sub.low, the low battery condition is decided.
In the foregoing description, the timing of every typing operation is referred to the timing of which the same load is periodically applied, such as during the paper feed operation at printing of a plurality of cut papers. Also, the predetermined value X.sub.low is in advance stored in a mask ROM or EEP-ROM in the apparatus, and, in such a ROM, a variety of data for controlling the printing operation, in addition to the threshold value of low battery, are stored.
Most of the recent recording apparatus are provided with functions such as high resolution printing or low noise drive, and requirements for the power supply system, particularly for safety thereof, have been becoming severe. Accordingly, the low battery detection is also required to be performed with relatively high accuracy.
However, there have been the problems relating to detection accuracy in the low battery detecting construction.
When the foregoing construction is equipped in the products of mass production, printers having dispersion in detection accuracy based on the ability tolerance of used components in every location ranging from "voltage observation" to "low battery analyzing system", to produce an undesired factor to decrease the low battery accuracy. Namely, even between the products of the same model, the products which correctly detect the voltage drop condition of a low battery are mixed with those which do not correctly detect the same condition.
In other words, there has been a fear of mis-recognition of low battery detection to perform printer operation regardless of the state of low electromotive force of the battery, and therefore the above-mentioned function could not be sufficiently achieved.
Such a mis-recognition of the low battery state caused by the detection error can lead to an erroneous operation control of products, which can connect with some of disadvantages. For example, in the case of a battery power driven printer, if a proper detection of the battery is not be performed, sometimes a sudden stop of the printing operation can occur halfway in the cut paper during printing.
In addition, for fine adjustment of the detection mechanism, usually a trimmer potentiometer (variable resistor) is used. This method requires a mechanical adjustment for every product, thereby involving a troublesome manual operation in production.
In summary, in view of production process, there has been until recently no way for the equipment of a high precision battery detection mechanism, which is indispensable for realizing a high performance printing, in a recording apparatus through an efficient method.